A sewing apparatus operates by piercing fibers or threads into a base fabric with needles. A sewing apparatus typically includes a needle which receives thread through its eye from a source of thread which may be mounted on the body of the sewing machine or remotely therefrom. The thread generally follows a path through various thread guides or guide plates on the machine, through a thread tensioning device, a thread take-up device, and then through other guide means mounted above the needle. The thread is then directed through the eye of the needle. The take-up device pulls the thread tight between the needle and the thread tensioning device. While the sewing apparatus is in operation, a threaded needle moves in a reciprocal fashion and continually inserts thread into a passing base fabric.
An example of a sewing apparatus includes a carpet tufting apparatus having a needle bar carrying a plurality of needles for inserting yarns carried by said needles into a base fabric for producing loops of yarns. The loops of yarns can be formed into loops of different heights or cut to form cut loop carpet.
A common problem associated with any sewing apparatus is the detection of thread breakage during operation before the broken thread is sewn or inserted into the base fabric. For example, during the carpet tufting process, when one of the multitude of yarns breaks while the carpet tufting apparatus is in operation, the eventual absence of thread in the corresponding needle creates a gap defect, or “mend,” in the carpet. A relatively short mend, such as less than 0.5 meters, in a carpet sample can be corrected using a hand-held device, but longer mends are much more difficult—or even impracticable—to fix. Thus, yarn breakage often results in carpet waste, which increases the ultimate cost of production.
To reduce the length of a mend, reduce the number of mends, or prevent mends in a sewing article, the sewing apparatus must stop operating as soon as possible after a thread breaks. Various types of thread breakage monitoring devices have been developed for stopping a sewing apparatus—or at least providing a warning signal—after thread breakage has been detected.
A variety of optical devices have been used in an attempt to effectively detect thread breakage. Two examples of such devices can be found in U.S. Pat. No. 4,625,666 to Sick and U.S. Pat. No. 4,691,647 to von Stein. Generally, such devices attempt to detect thread breakage by projecting a light beam near or onto the threads of a sewing apparatus. These devices are typically grouped into two categories: light-on and dark-on. When a thread breaks and either falls into (dark-on) or out of the light beam (light-on), a photo-sensor detects a change in the light beam and sends a signal to a controller or alarm indicating thread breakage.
In typical dark-on optical sensing systems, a light beam is positioned near a thread or a bank of threads such that a photo-sensor receives a generally continuous beam of light while the threads are intact. When a thread breaks and passes or falls through the path of the light, the thread temporarily interrupts the light beam. The photo-sensor detects this interruption in the light beam—i.e., a quantity of light lower than a predetermined threshold quantity of light—and sends a signal indicating that the light beam has been interrupted or broken.
The closer the light beam is positioned to a thread, the greater the likelihood a broken thread will interrupt or fall through the light beam. To position the light beam closely to the thread normally requires that the optical device be attached or mounted directly to the sewing apparatus. The size of known thread breakage detection devices—in particular the photo-sensor emitters and receivers of these devices—prevents placement of the light beam in positions near the threads, which would help ensure or increase the consistency of thread breakage detection.
Further reducing the accuracy and consistency of thread breakage detection is the vibration typical of sewing apparatuses. Vibration of sewing apparatuses—especially those used on an industrial scale—is common. Such vibration often jars the light emitter and/or receiver of the optical thread breakage detection device out of alignment. Not only does such misalignment interrupt the production process, but misalignment can often be difficult to detect, resulting in mend defects.
Known optical thread breakage detection systems also require precise alignment to consistently and accurately detect thread breakage. Machine vibration further reduces the accuracy and consistency of such systems. Thus, there is a need for an optical thread breakage detection apparatus that can be positioned near the thread of a sewing apparatus and that also is generally less susceptible to misalignment caused by machine vibration.